“If at first you don’t succeed, keep on sucking till you do succeed” – Curly Howard. Thankfully, we don’t have to be a Stooge by not meeting customer expectations. We can clearly see that the failure to understand common flexographic print issues is costly. The good news: productivity, down press time and excessive waste can be minimized or avoided altogether with a bit of observation and corrective action.

I would like to take the next few pages to lay out many recognized defects and outline their possible causes, as well as point you in the direction of a proper response. While this is not an exhaustive list, I’ve tried to include as many routine issues as I can in a short amount of time. Just think of the following as a troubleshooting guide for common possible solutions spanning a wide range of printing and packaging problems. Let’s get right to it:

Problem	Problem Causes	Corrective Action
Poor Ink Adhesion to substrate	Improper ink formula / chemistry	Check with your ink supplier to make sure the correct ink is being used for each substrate
	Ink thinned out too much, poor binding agent	Stabilize viscosity, add fresh ink or binding resin
(Ink fails tape test)	Dyring issues, low temperature or air flow	Increase drying temp or air velocity
(Ink fails crinkle test)	Low surface treatment on substrate	Check substrate surface and varnish being used
Ink fails scuff test	Substrate could be contaminated	Check correct material being used with supplier, may need wash coat before print
	Substrate may require treatment	Primer may be needed

Binding, Gear Marks, Chatter	Web tension	Adjust web tension and check web control system, clean and lubricate rollers
(Dark lines across web and density variation)	Gears bottoming out	Make sure plate and mounting undercut matches gear, too much squeeze
	Plate slur	Use barrier bars outside print area
	Ink viscosity too high	Check and maintain viscosity frequently
	Stickyback and plate durometer	Match tape cushion and plate durometer with print application
	Anilox and plate cylinder/sleeve TIR	Check concentricity of anilox and print carriers

Bleed (Undercolor / trapping of color)

Colors drying too slow or too fast

Check viscosity and ink film thickness, use faster or slower solvents

Blocking	Trapped solvent	Adjust drying condition, check solvent balance
	Improper pH and viscosity levels	Check and maintain viscosity/pH balance periodically

Halo	Too much plate pressure	Correct pressure setting, Kiss impression
(Line around printed area, double-edged print)	Cupped edges on plate	Make new plates
	Plate cylinder out of round, poor TIR	Inspect cylinder and possible wear of gears and bearings
	Plate or tape durometer too high	Use softer plates and tapes
	Too much ink applied	Check or lower anilox volume
	Print cylinder and substrate at different speeds	Check and maintain proper web to cylinder speed

Out of Register	Plate not mounted in register	Check mounting and sleeve defects
	Uneven pressure between CI and plate cylinder	Adjust correct pressure
	Drive gear damaged	Replace gear
	Idle rolls drag or rotate differently	Replace or lubricate idle roll bearings

Picking	First color too slow, second color too fast	Check drying conditions
(Ink transfers to subsquent plates)	High viscosity of second color	Increase press speed, lower viscosity of second color
	Too much pressure of plate to substrate	Use Kiss impression

Pinholing	Anilox wear	Conduct audit from anilox supplier, replace or re-engrave anilox
(Small holes in solids)	Ink drying too fast	Adjust solvents, add retarder
	Wrong anilox selection	Use 60º anilox angle
	Dirty central impression cylinder	Clean CI drum
	Ink does not form homogenous uniform film	Increase film thickness, check dilution rate of ink, check anilox pressure
	Rough surface of substrate	Consult substrate supplier

Bridging	Anilox volume too high or line count too low	Adjust volume and anilox lpi
(Dots connecting to each other)	Too much pressure	Adjust pressure between print cylinder to anilox
(Adhesion between two surfaces)	Excessive pressure in rewind	Reduce rewind tension
	Web too warm during rewind	Lower drying tunnel or lower chill roll, check room temperatures
	Web wound with moisture	Avoid over chilling, room humidity

Dot Gain	Print pressure too high	Lower print cylinder pressure, kiss impression
	Improper stickyback	Check cushion density to match print application
	Poor ink metering	Use chamber doctor blades and proper installation
	Printing plate not correct size or swollen	Check plate thickness
	Incorrect viscosity or anilox volume	Maintain proper viscosity settings, lower anilox volume
	Dirty impression and/or plate cylinder	Trapped air under plate, clean impression and plate cylinders

Ink Drying Too Fast	Improper use of solvents	Refer to you ink supplier for proper balance
(Ink dries on plate or anilox, fails to transfer to substrate)	Air movement near plate and anilox	Eliminate air movement fans, windows/doors, dryers
	Low pH (water based ink)	Check pH level, optimum balance between 8.8 – 9.2
	Dried ink on plates	Wash plates after setup, too much air movement
	Pressroom temps too high or low humidity	Control pressroom environment

Ink Drying Too Slowly	Use of slower drying solvents	Use faster drying solvents
(Improper trapping, Ink is picking, tacky print surface, ink penetrating into paper)	Excessive ink film thickness	Check anilox volume
	Viscosity too high	Maintain proper viscosity balance
	Excessive press speed not allowing for proper drying	Adjust press speed

Feather	Improper anilox and plate pressure	Decrease pressure
(Irregular edges around print area)	Dried ink on plate or anilox, ink buildup around dots	Clean plates, apply proper anilox and plate pressure, cover ink pans/buckets
	Static	Use anti-static devices
	Surface tension not transferring ink correctly	Check substrate dyne levels
	Poor dots	Check shoulder supporting the dot
	Viscosity too high for screen printing	Maintain proper viscosity levels

Wringling	Non-uniform substrate thickness	Replace roll
(Wrinkles in substrate)	Equipment not aligned properly	Adjust all rollers to proper set up and alignment

Of course, there are many variables in flexo printing and I can’t get into every possible issue here, but in my experience these are the most common problems and they often have very simple solutions. Just remember that when you invite trouble by overlooking maintenance and observation, it is usually quick to adapt, costing you time and money. Don’t wait when it’s so easy to get ahead of the ball before things fall apart!

One last note to leave you with: it’s worthwhile to bring technology and automation into the conversation here because they can assist in monitoring and sustaining your optimal press conditions in hugely impactful ways. For instance, GAMA systems are capable of controlling and automatically maintaining pH, viscosity and temperatures. Grafikontrol can assist in color monitoring, web viewing / print defection, registration and waste management. As a rule of thumb: when in question, it is always best to consult with your suppliers. After all, that’s what we’re here for.

Dan Dietrich
Bingham Flexo Services
Technical Sales
dan.dietrich@binghamflexoservices.com